Altitudinal timberlines are thought to be moving upward as a result of global climate change. Takahashi et al.evaluate how the timberline has formed in a zone between 2350–2600 m in central Japan where the conifer Abies mariesii and the deciduous broadleaved Betula ermanii dominate above the timberline and the dwarf pine Pinus pumila dominates below it. Measurements of trunk-diameter growth rate, mortality and mechanical damage suggest that the altitudinal location of the timberline is mainly affected by mechanical damage due to strong winds and snow rather than by growth limitation due to low temperatures.